1. Field of the Invention
This invention generally relates to a system and method for authenticating image signals whether they are still images or part of motion picture video. A system designed according to this invention provides a digital signature unique to the image and embeds coded information corresponding to that signature into a transform representation of the image.
2. Description of the Related Art
Digital imaging is being used at an increasing rate. Two standards for handling compressed digital image information include JPEG, which is typically used for still images, and MPEG, which is typically used for motion picture video.
The JPEG compression standard is described in “The JPEG Still Picture Compression Standard”, by Gregory T. Wallace, Communications of the ACM, April 1991, vol. 34, No. 4, pp. 31–44, which is incorporated into this specification by reference.
The MPEG standard is commonly used for motion picture video compression. MPEG is described in Practical Digital Video With Programming Examples In C, by Phillip E. Mattison, John Wiley and Sons, 1994, chapter 11, pages 373 through 393, and in “MPEG: A Video Compression Standard for Multi-Media Applications”, by Didier Le Gall, Communications of the ACM, April 1991, vol. 34, no. 4, pps. 47 through 58, all of which are incorporated into this specification by reference.
As the use of digital imaging increases, the need for handling the image information in new ways also increases. One example is the need for image authentication in circumstances where the image information is used for surveillance or other situations where the integrity of a received image signal is critical. Whether image signals are captured and stored in memory for later observation or are transmitted over a network to a central location for real time observation, it is possible for unauthorized individuals to manipulate the stored images or to tamper with the signal being sent over the network.
While some attempts have been made to provide enhanced handling of image information, none has addressed the need for a secure authentication system. For example, the published application GB 2,326,048 discusses a system for embedding a digital watermark into compressed image data. The digital watermark, however, merely indicates copyright or other author identification information. The disclosure of that document does not include sufficient security measures to authenticate the content of an image signal.
Those skilled in the art have been endeavoring to develop new methods for ensuring the integrity of transmitted signals. One area where advances have been made is the derivation of a digital signature for an image based upon the image data. This invention utilizes a digital signature extraction method combined with embedding the digital signature information into a transform representation of the image. At a receiving location, the embedded information can be deciphered and compared with the expected image signature so that the integrity of the received signal can be verified.